Here the 1837 edition replaced their with the. This change was not marked by Joseph Smith in his editing of the printer’s manuscript for the 1837 edition. It is possible that the use of the pronoun it for the city of Ammonihah (“in one day it was left desolate”) seemed to clash with the use of the plural their, although in reality there is no difficulty at all in interpreting this pronominal form since their and they are used in the immediately preceding verse:
The 1837 replacement of their with the was most probably a typo. The use of their adds cohesion to the narrative and will be restored in the critical text.
Summary: Restore in Alma 16:10 the possessive pronoun their in “their carcasses were mangled”, the original reading.